A Comparison of Polymer Flooding With In-Depth Profile Modification

Abstract

For stratified reservoirs with free crossflow and where fractures do not cause severe channeling, improved sweep is often needed after water breakthrough. For moderately viscous oils, polymer flooding is an option for this type of reservoir. However, in recent years, an in-depth profile-modification method has been commercialized in which a block is placed in the high-permeability zone(s). This sophisticated idea requires that (1) the blocking agent have a low viscosity (ideally a unit-mobility displacement) during placement, that (2) the rear of the blocking-agent bank in the high-permeability zone(s) outrun the front of the blockingagent bank in adjacent less-permeable zones, and that (3) an effective block to flow form at the appropriate location in the high-permeability zone(s). Achieving these objectives is challenging but has been accomplished in at least one field test. This paper investigates when this in-depth profile-modification process is a superior choice over conventional polymer flooding.Using simulation and analytical studies, we examined oilrecovery efficiency for the two processes as a function of (1) permeability contrast, (2) relative zone thickness, (3) oil viscosity, (4) polymer-solution viscosity, (5) polymer-or blocking-agent-bank size, and (6) relative costs for polymer vs. blocking agent. The results reveal that in-depth profile modification is most appropriate for high permeability contrasts (e.g., 10:1), high thickness ratios (e.g., less-permeable zones being 10 times thicker than high-permeability zones), and relatively low oil viscosities. Because of the high cost of the blocking agent relative to conventional polymers, economics favours small blocking-agent-bank sizes (e.g., 5% of the pore volume in the high-permeability layer). Even though short-term economics may favour in-depth profile modification, ultimate recovery may be considerably less than from a traditional polymer flood.

Flow of a Cross-Linking Polymer in Porous Media

“…In addition to that, porosity reduction and the change in the dispersion coefficient were obtained by the injection of a tracer into the core (before and after XL polymer injection). Tracer transport in porous media was modelled by fitting an experimental breakthrough curve for a tracer with a one-dimensional advection-dispersion model, where porosity and dispersion are matching parameters (Sorbie 1991;van der Hoek et al 2001;Seetha et al 2014). The two tracer tests show a porosity reduction of 6% and an increase in the dispersion coefficient by a factor of 20 which indicates that the in situ cross-linking took place in the porous media.…”

“…In-depth profile modification is a promising technology for improving the sweep efficiency of water flooded heterogeneous oil reservoirs (Seright et al 2011;Sydansk and Southwell 2000;Bailey et al 2000;Glasbergen et al 2014). It can be implemented by injecting a crosslinking polymer (XL polymer) that propagates deep into the reservoir.…”

“…2). The efficiency of the process depends on the geological characteristics of the reservoir, the physical properties of the cross-linking polymer, its concentration in the target zone and the interaction with the minerals of the rock (Seright et al 2011;Bailey et al 2000;Glasbergen et al 2014;Lake 2010). The most appropriate chemical system for in-depth profile modification in a reservoir should have the following properties: tolerance to the salinity of the brine, thermal stability, low initial viscosity, deep propagation into a reservoir, and low mechanical degradation (Karsani et al 2014;Zhang and Zhou 2008;Zitha et al 2002).…”

A critical review on use of polymer microgels for conformance control purposes

“…Proponents believe that microgels will primarily invade these high permeability zones as long as the microgel solution/gelant is of low viscosity; it is thought that the microgel solutions would essentially act as water does during injection. This, as well as steric effects, would minimize their penetration into other less permeable zones (Cozic et al, 2009;Seright et al, 2011). Another possible reason for minimal microgel penetration of low permeability layers is the relatively large microgel size (Zaitoun et al, 2007).…”

Effect of a polymer on chromium(III) diffusion during gelant injection in fractured media

“…5,6 The water-plugging performance of polymer gel systems in heterogeneous reservoirs is satisfactory, but it is unfavorable when they are used in fractured reservoirs. Seright and coworkers [6][7][8][9] have investigated the plugging performance of polymer/Cr 31 gels in fractures for many years. They found that the diffusion loss of chromium from gelant to brine could greatly reduce the gel strength or even make the gelant ungelled, and finally, it resulted in plugging ineffectiveness.…”